1. Field of the Invention
This invention is concerned with the manufacture of prefabricated tape material designed to be applied on and secured to roadway pavements and other roadable surface for forming traffic dividing and regulating lines and other signs, and to the tape material manufactured by making use of a new and improved method as hereinbelow described. More particularly, the invention is concerned with roadway surface sign forming retroreflective tape material and with a method for producing same.
The term "retroreflective" as hereinafter used in this description and in the appended claims is intended to designate the property of the tape material and more particularly of systems and means forming part of the and secured to its upper or exposed face, which will reflect an incident beam or ray of light in such a manner that a brilliant beam is returned to the source of light, generally a vehicle headlamp system, and therefore towards the vehicle's driver eyes, even if the incident light strikes the surface of the sign and therefore the road surface, at a very small angle (the so called "grazing light"). This property sharply improves the nighttime and bad weather visibility of the sign, when the service of headlamps is required for safety.
2. Description of the Prior Art
Road surface sign-forming retroreflective tape materials are known in the art and extensive comments thereabout are unnecessary, as this art is a well known and worked one. In the specification of the U.S. Pat. No. 3,587,415, granted to the instant applicant, the utility and the principles od retroreflective tape materials have been set forth. This art has been consistently improved and more efficient retroreflective systems have been devised and secured to sign-forming prefabricated tape materials or to signs otherwise formed on road surfaces, such as by painting, by pouring and doctoring hardenable molten or otherwise settable compositions and so on. For example, a number of successively improved retroreflective elements and systems have been disclosed and extensively commented in the patent and technical literature, more particularly in my prior U.S. Pat. Nos. 3,781,083, 3,894,791, 3,964,820, 3,964,821 and 3,981,557.
Generally, each retroreflective element or system comprises a nearly globular or spherical transparent body, partially embedded into the sign-forming tape surface layer (such as of polyurethane or other traffic wear resisting polymeric composition) such as a part-spherical surface bulges above the sign surface, while the lower and embedded portion of said body has reflective means secured adjacently thereto. The light rays which impinges upon the bulging surface is refractively dowardly deviated in said body and strikes on the reflective means for being finally returned along a path nearly close and parallel to that of incidence, towards the source of light. The optical phenomena involved in the retroreflection have been widely commented in the above indicated prior patents, wherein critical data such as relating to indexes of refraction and to various components relationships are also disclosed.
It is an object of this invention to provide a new and further improved retroreflective road surface sign-forming tape material associated to particularly efficient retroreflective elements or systems. Another object of the invention is to provide and advantageous manner for manufacturing such elements or systems and for associating same to a tape material as above.